1. Field of the Invention
The present invention relates to a polyamide composition which includes an alkylene oxide group-containing polyetheramide or polyetheresteramide and a metal salt, and more particularly to a polyamide composition with long lasting antistatic properties and a lower surface resistivity than the polyamide alone.
2. Description of the Prior Art
To impart a polymer with antistatic properties is often achieved by adding an antistatic agent. Antistatic agents can be categorized into two groups: those with low molecular weights, for example, conventional surfactant-type antistatic agents; and those with high molecular weights. After being added into a polymer, the antistatic agent with a low molecular weight will easily migrate to the polymer surface and thus deteriorate the properties of the polymer. In some cases, the antistatic property will be lost by washing or wiping. On the other hand, owing to their polymeric structure, antistatic agents with high molecular weights are compatible with other polymers, and thus, the second group of antistatic agent has long lasting antistatic properties.
Conventional antistatic agents with high molecular weights suitable for polyesters or polyamides are normally categorized into two groups. One group is formed by using a sulfonate or a polyethylene oxide (PEO) with a high molecular weight coated on the surface of the polymer or added inside the polymer. For example, in Japanese Patent No. 5,262,460, a PET (polyethylene terephthalate) is blended with a PEO of 5000 g/mole to 16000 g/mole to obtain an antistatic resin. In U.S. Pat. No. 5,010,193, a PET is blended with an ethylene oxide copolymer of 2000 g/mole to 50000 g/mole to improve the antistatic property and compatibility. In U.S. Pat. Nos. 5,194,327 and 5,182,169, a sulfonate with a high molecular weight is coated on the surface of a polyester to correct the disadvantages in the antistatic agent with a low molecular weight, such as opacity and surface cake. Thus, the antistatic property is enhanced.
In the other group, the polyester is modified with a PEO or a sulfonate to improve the hydrophility and to obtain the antistatic polyester. For example, in U.S. Pat. Nos. 5,130,073, 5,064,703, 4,713,194, and 4,506,070, a polyester is condensed with a PEO to, obtain a hydrophilic polyester. However, due to the incomplete reaction between EO and diacid, an antistatic agent with a high molecular weight is not easy to form.
In U.S. Pat. Nos. 4,943,510, 5,051,475, and 4,468,433, a polyester is reacted with a dicarboxy phenyl sulfonate to obtain a hydrophilic polyester. However, the physical and antistatic properties of the polymers are poor.
In U.S. Pat. No. 4,872,910, a conductive composition includes at least one metal crosslinking latex binder and a metal salt/polyethylene oxide complex. However, the compatibility of the polyethylene oxide with the latex binder is poor, and the conductive composition has poor antistatic properties.
In U.S. Pat. No. 5,882,800, an antistatic composition includes a polyester/polyalkylene oxide copolymer and a lithium salt. In U.S. Pat. No. 5,122,303, an ion-conducting composition includes a polyester/polyether copolymer and a lithium salt. However, there is still a need to decrease the surface resistivity of an antistatic composition.